Field of the Invention
The present invention relates to a bipolar high-voltage power component having a semiconductor body on which at least two mutually spaced apart electrodes are provided, between which a drift path is formed in a semiconductor region of a first conduction type.
In the case of bipolar semiconductor components such as, for example, diodes, bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors), their dynamic response is determined to a very great extent by the minority charge carriers present in the drift path, that is to say in the base, in the case of a bipolar transistor. That is because the smaller the base width, the higher the limiting frequency that can ultimately be achieved.
It has recently become possible to reduce the base width of bipolar transistors down to approximately 30 nm, which leads to the aforementioned reduction in stored minority charge carriers in the base, so that an increase in the limiting frequency would be possible. Thus, it has been shown that when the base width of bipolar transistors is reduced down to about 30 nm, the quantity of stored minority charge carriers in the base and/or the diffusion capacitance can be reduced, which ultimately leads to a corresponding increase in the limiting frequency up to approximately 50 GHz, but at the same time the dielectric strength is reduced to a few volts.
In the case of high-voltage power components such as IGBTs, for example, across which there may be a voltage of up to several kV, or in the case of diodes, the base width is inherently determined by the required dielectric strength and the structure of the high-voltage power components. However, it is the case quite generally that the minority charge carriers stored in the drift zone, that is to say the minority charge carriers stored in the base zone in the case of a bipolar transistor, limit the maximum operating frequency or give rise to dynamic losses when the component is switched on and off.
Although it is possible to reduce dynamic losses in bipolar high-voltage power components by reducing the quantity of stored minority charge carriers by reducing the emitter efficiency in the case of an IGBT, for example, such a procedure nonetheless inevitably leads to an increase in static losses. It is also possible to reduce the lifetime of charge carriers by doping with a corresponding lifetime killer, that is to say, for example, gold or platinum, or by electron or helium irradiation, whereby dynamic losses can be reduced.
However, such a procedure also leads to a simultaneous increase in the static losses.
It is accordingly an object of the invention to provide a bipolar high-voltage power component, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which, despite a relatively large drift path, switching losses are considerably reduced and thus possible operating frequencies are considerably increased, without adversely affecting on-state properties of the bipolar high-voltage power component.
With the foregoing and other objects in view there is provided, in accordance with the invention, a bipolar high-voltage power component, comprising a semiconductor body having a semiconductor region of a first conduction type; at least two mutually spaced apart electrodes disposed on the semiconductor body and forming a drift path between the electrodes in the semiconductor region; and floating zones of a second conduction type opposite the first conduction type, the floating zones preferably disposed in the semiconductor region and extending from the vicinity of one of the at least two electrodes as far as the vicinity of another of the at least two electrodes, the floating zones respectively emitting charge carriers of the second conduction type into the semiconductor region or taking up the charge carriers of the second conduction type from the semiconductor region, when the power component is respectively switched on or switched off.
Therefore, in the case of the bipolar high-voltage power component according to the invention, a xe2x80x9ccompromisexe2x80x9d between dynamic and static losses (with the dielectric strength unchanged) is avoided. To that end, floating zones of the second conduction type, that is to say p-conducting zones, are inserted by diffusion or implantation into the semiconductor region of the first conduction type, that is to say, for example, to an n-conducting drift path of a bipolar transistor. These floating zones, which can also be referred to as xe2x80x9cp-type pillarsxe2x80x9d in the case of an n-conducting semiconductor region, have the task of introducing the minority charge carriers, that is to say holes in the present example, through xe2x80x9cohmic conductionxe2x80x9d into the semiconductor regions situated between the floating zones, or of conducting away those minority charge carriers from the semiconductor regions.
It has been shown that this operation, namely the introduction of minority charge carriers into the semiconductor regions from the floating zones during switch-on and the removal of the minority charge carriers from the semiconductor regions into the floating zones during switch-off, can take place much more quickly than the build up and the reduction of the minority charge carrier density by diffusion.
In accordance with another feature of the invention, the floating zones are connected, through a respective MOS transistor with a channel of the second conduction type or a bipolar transistor with a base of the first conduction type, to active regions of the power component which are connected to the two electrodes. Thus, by way of example, in the case of an IGBT with an n-conducting semiconductor region as a drift path, p-conducting pillars are connected through a pnp transistor to the emitter or the anode of the IGBT and through a p-MOS transistor to the channel or body region of the IGBT. When the IGBT is switched on, the holes are then transported through the pnp transistor and the p-conducting pillars into the drift path, while in the event of switch-off, the p-MOS transistor is switched on, with the result that the minority charge carriers, that is to say the holes, can flow away from the n-conducting semiconductor region through the p-conducting pillars as majority charge carriers and the p-MOS transistor.
In accordance with a further feature of the invention, the MOS transistor is to be connected together with a further MOS transistor containing the corresponding active region. In this case, in particular, the gates of the two MOS transistors can be connected to one another. In the above example, then, the gate of the p-MOS transistor, through which the minority charge carriers flow away from the drift path, is connected to the gate of an n-MOS transistor.
In accordance with an added feature of the invention, depending on the operating frequency, it may then be expedient, in order to reduce the switch-off losses, to switch e the p-MOS transistor on first and then switch the n-MOS transistor off with a delay of 1 xcexcs, for example. This delay can be achieved by separate driving or else by a delay element, for example a high-value resistor between the two gates. In this case, the delay element may also be integrated in the semiconductor chip of the bipolar high-voltage power component.
In accordance with an additional feature of the invention, the dopings of the semiconductor region and of the floating zones are set in such a way that the semiconductor region and the semiconductor zones xe2x80x9ccompensatexe2x80x9d one another, in order thus to be able to achieve high reverse voltages. Dopings of between 5xc3x971014 and 5xc3x971016 charge carriers cmxe2x88x923 are preferably chosen in this case.
However, it is not essential in this case to achieve the highest possible n-type doping in, for example, an n-conducting semiconductor region as in the case of a unipolar transistor. Instead, the resistance of the floating semiconductor zones, that is to say of the p-conducting pillars in the above example, should be matched in such a way that the holes flow away sufficiently rapidly at a voltage that is still low. This is because the charge carrier flooding, which is necessary for good conductivity in the on state, is then made available by the p-conducting emitter and is not adversely influenced by the p-conducting pillars, since these p-conducting pillars are not connected to an extracting p-conducting region in on-state operation, which occurs only during switch-off by the p-MOS transistor.
In accordance with yet another feature of the invention, the invention can be applied with particular advantage to an IGBT since, in this case, particularly high flooding with charge carriers occurs. The charge carriers can then immediately be removed through the floating zones. It has been shown that an IGBT constructed according to the present invention has switch-off losses reduced by up to 80% as compared with conventional IGBTs, given the same forward voltage. Even when compared with a so-called xe2x80x9cfield stop IGBTxe2x80x9d, the switch-off losses can still be halved by the invention.
In accordance with a concomitant feature of the invention, further possibilities for application of the bipolar high-voltage power component according to the invention are diodes, for example. In diodes, the floating regions can also be connected directly to the p-conducting region of the anode, so that an additional p-MOS transistor is not required.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a bipolar high-voltage power component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.